Generally, a throttle body of an intake system of an engine is provided with an ISCA (Idle Speed Control Actuator) such that the engine can also be supplied with intake air while driven in an idling state, that is a state where a throttle valve is closed.
Conventional throttle bodies are connected to an upstream side of a surge tank through a main passage. A throttle valve is rotatably mounted in the main passage such that supply of the intake air can be controlled thereby. The ISCA typically is connected by a bypass passage to the throttle body. The inlet of the bypass passage is generally located in front of the throttle valve, and the outlet of the bypass passage is located in rear of the throttle valve such that air can bypass the throttle valve and be drawn to the engine in an idle state. A solenoid valve may be provided to control the intake air through the bypass passage.
Generally, the output end of the bypass passage is perpendicularly connected to the main passage. Accordingly, when the throttle valve is opened for engine acceleration and the solenoid valve is open for the control of bypass air, the bypass air through the bypass passage is drawn and accelerated by the intake flow moving rapidly through the main passage to create a Venturi tube effect. Such an aerodynamic effect in an intake system of an engine can cause a noise like a piping sound, and such a noise deteriorates the quality of a vehicle.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.